For example, as disclosed in Patent Literature 1 and Patent Literature 2, projectors using a coherent light source are widely used. For coherent light, laser light oscillated from a laser light source is typically used. If image light from a projector is formed by coherent light, speckles are observed on a screen that is irradiated with the image light. Speckles are perceived as a dot pattern and deteriorate display image quality. In Patent Literature 1, the incident angle of the image light incident on each position on the screen is temporally changed for the sake of reducing speckles. As a result, uncorrelated scattering patterns occur on the screen, and speckles can be reduced by the superposition of the scattering patterns.